A catalyst and catalytic converter for zero emission of N2O from gasoline engines

Abstract

The application discloses a kind of catalyst and catalytic converter of gasoline engine N2O zero emission, the catalyst is with Rh as main catalyst, CeO2 as auxiliary catalyst, with graphene / molecular sieve as the coating of multilevel structure after graphene is modified to molecular sieve, honeycomb cordierite ceramic as carrier.The catalytic converter is designed by catalyst packaging.By the design of the multilayer staggered structure of graphene / molecular sieve, the adsorption and diffusion time of N2O is prolonged, the adsorption amount of N2O is increased, so that the catalytic converter has sufficient ignition time.Through the modification of graphene to molecular sieve, the thermal stability, hydrothermal stability of molecular sieve are further ensured, and the working condition requirements of gasoline engine are met, so that the shape selective adsorption and catalysis of N2O are realized, and the zero emission target of N2O is achieved.

Description

Technical Field

[0001] This application relates to the field of gasoline engine exhaust gas treatment technology, and in particular to a catalyst and catalyst device for zero N2O emissions from gasoline engines. Background Technology

[0002] Nitrogen gas (N2O) is a colorless gas with a sweet taste and anesthetic properties. As a trace gas, N2O contributes 21 times more to the greenhouse effect than CH4, and its global warming potential (GWP) is 310 times that of CO2. A doubling of atmospheric N2O concentration will lead to a global temperature increase of 0.3°C. N2O is very stable, with a residence time of up to 120 years. Therefore, the atmospheric environmental damage caused by N2O emissions is extremely serious.

[0003] Atmospheric nitrogen (N2O) mainly originates from agriculture, industry, fossil fuel combustion, biomass combustion, wastewater, and municipal waste, with agriculture accounting for more than two-thirds of global N2O emissions. Global transportation emissions account for approximately 3 ± 1% of current estimates of total anthropogenic emissions. Domestic research on greenhouse gas emissions from motor vehicles also indicates that light passenger vehicles and gasoline vehicles are the main sources of N2O emissions from motor vehicles.

[0004] Because N2O has low reactivity and hardly reacts with most known gases in the atmosphere, its treatment is extremely difficult. The activation, dissociation, and degradation of N2O constitute a challenging task for both research and engineering applications. Currently, effective treatment of N2O in gasoline engine exhaust is lacking. Summary of the Invention

[0005] To address the problem that existing three-way catalytic converters for gasoline engines cannot achieve zero N2O emissions, this invention proposes a catalyst and catalytic converter for zero N2O emissions in gasoline engines, enabling the N2O emissions after the three-way catalytic converter to achieve the goal of zero emissions.

[0006] The present invention provides a catalyst for zero N2O emissions in gasoline engines, wherein the catalyst is mainly composed of Rh and co-catalyst, and uses graphene / molecular sieve modified with graphene as a multi-level coating and honeycomb cordierite ceramic as a carrier.

[0007] Preferably, the coating sequence on the cordierite carrier is a multi-level structure of graphene / molecular sieve / graphene, and the channel surface layer is graphene.

[0008] Preferably, the coating sequence on the cordierite carrier is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is a molecular sieve.

[0009] Preferably, the cordierite carrier is divided into two parts along the channel direction. The coating sequence of the front part is a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer is graphene. The coating sequence of the rear part is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is molecular sieve.

[0010] Preferably, the cordierite carrier is divided into two parts along the channel direction. The coating sequence of the first half is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is molecular sieve. The coating sequence of the second half is a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer is graphene.

[0011] Furthermore, the Rh catalyst and CeO2 co-catalyst are directly coated on the surface of graphene or molecular sieve channels.

[0012] Preferably, the Rh catalyst and CeO2 co-catalyst are also coated on the surface of the graphene or molecular sieve inside the structure.

[0013] The present invention also provides a method for preparing the above-mentioned catalyst, comprising the following steps:

[0014] The methods for modifying molecular sieves with graphene are as follows:

[0015] 1) Using the in-situ hydrothermal synthesis method, the honeycomb cordierite ceramic carrier is placed in the prepared molecular sieve precursor solution for in-situ crystallization, so that the molecular sieve is directly "grown" on the carrier to obtain a molecular sieve coating.

[0016] 2) Calcium hydrate was added directly to the aqueous solution of graphene oxide, and then the graphene solution was prepared by hydrothermal reduction, resulting in a graphene solution that was uniformly and stably dispersed in water.

[0017] 3) The honeycomb cordierite ceramic carrier with molecular sieve coating is placed in a graphene solution, and the graphene is highly dispersed into the surface and channels of the molecular sieve by ultrasonic impregnation method, thereby completing the surface and channel modification of the molecular sieve and obtaining the graphene / molecular sieve coating after the graphene-modified molecular sieve.

[0018] 4) Further, by repeating the above steps, a multi-layered coating structure can be obtained.

[0019] The present invention also provides a catalyst for zero N2O emissions in a gasoline engine, which is encapsulated from the above-mentioned catalyst.

[0020] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0021] (1) The multi-level interlaced structure of graphene / molecular sieve significantly increases the contact area between the catalyst and N2O, which can increase the adsorption amount of N2O.

[0022] (2) The multi-level interlaced structure of graphene / molecular sieve significantly increases the space of the internal nanopore structure of the catalyst, which can increase the molecular diffusion path of N2O in the nanopore and prolong the adsorption and diffusion time of N2O.

[0023] (3) The multi-level interlaced structure of graphene / molecular sieve can improve the thermal conductivity and thermal diffusion performance of the catalyst, and rapidly increase the internal temperature of the N2O catalyst under the low temperature starting condition of the engine, so that the catalyst has sufficient ignition time.

[0024] (4) The small-pore molecular sieve has a crystalline structure, which can ensure the thermal and structural stability of the molecular sieve. The modification of the molecular sieve with graphene can further ensure the thermal and hydrothermal stability of the molecular sieve, and meet the operating requirements of gasoline engines.

[0025] (5) Based on the structure and polarity of N2O, graphene is used to regulate the pore structure and adsorption performance of molecular sieves, so as to achieve shape-selective adsorption and catalysis of N2O and achieve the goal of zero emission of N2O. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the structure of the gasoline engine N2O zero-emission catalyst in this invention;

[0028] Figure 2 This is a schematic diagram of the structure of different multi-level coatings in the N2O zero-emission catalyst for gasoline engines in this invention;

[0029] Wherein, (a) indicates that the coating sequence on the cordierite carrier is a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer is graphene; (b) indicates that the coating sequence on the cordierite carrier is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is molecular sieve; (c) indicates that the cordierite carrier is divided into two parts along the channel direction, with the coating sequence of the first half being a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer being graphene; and the coating sequence of the second half being a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer being molecular sieve; (d) indicates that the cordierite carrier is divided into two parts along the channel direction, with the coating sequence of the first half being a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer being molecular sieve; and the coating sequence of the second half being a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer being graphene.

[0030] Figure 3 This is a schematic diagram of the different catalyst coating positions in the gasoline engine N2O zero-emission catalyst of the present invention;

[0031] Wherein, (a) indicates that the Rh catalyst and CeO2 co-catalyst are directly coated on the surface of graphene or molecular sieve channels; (b) indicates that the Rh catalyst and CeO2 co-catalyst are coated on the surface of molecular sieve / graphene according to the multi-level interlaced structure modified by molecular sieve / graphene.

[0032] Figure 4 A schematic diagram showing the polarity of some molecules in gasoline engine exhaust;

[0033] Figure 5 This is a schematic diagram of the shape-selective adsorption and catalysis of N2O by graphene / molecular sieve in the N2O zero-emission catalyst of this invention;

[0034] Figure 6 This is a schematic diagram of the structure of the gasoline engine N2O zero-emission catalyst in the gasoline engine exhaust aftertreatment system of the present invention;

[0035] Figure 7 This is a schematic diagram of the structure of the N2O catalyst for a gasoline engine in this invention;

[0036] Wherein, (a) represents the N2O catalyst; (b) represents the radial cross-sectional view of the honeycomb structure inside the catalyst; (c) represents the cross-sectional view of the central local axial channel; (d) represents the cross-sectional view of the boundary local axial channel; and (e) represents the local surface structure diagram of the channel.

[0037] Figure 8 A schematic diagram of the physical and chemical adsorption process of N2O in a gasoline engine N2O zero-emission catalyst;

[0038] Where (a) represents physical adsorption and (b) represents chemical adsorption. Detailed Implementation

[0039] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0040] A catalyst for zero N2O emissions in gasoline engines, such as Figure 1 As shown, the catalyst uses Rh as the main catalyst and CeO2 as the co-catalyst, with graphene / molecular sieve modified with graphene as the multi-layered coating and honeycomb cordierite ceramic as the carrier. The multi-layered structure is as follows: Figure 2-3 As shown.

[0041] In a more preferred embodiment, such as Figure 2 As shown in (a), the coating sequence on the cordierite carrier is a multi-level structure of graphene / molecular sieve / graphene, and the channel surface layer is graphene.

[0042] In a more preferred embodiment, such as Figure 2 As shown in (b), the coating sequence on the cordierite carrier is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is a molecular sieve.

[0043] In a more preferred embodiment, such as Figure 2 As shown in (c), the cordierite carrier is divided into two parts along the channel direction. The coating sequence of the first half is a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer is graphene. The coating sequence of the second half is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is molecular sieve.

[0044] In a more preferred embodiment, such as Figure 2 As shown in (d), the cordierite carrier is divided into two parts along the channel direction. The coating sequence of the front half is a multi-level structure of molecular sieve / graphene / molecular sieve, etc., and the channel surface layer is molecular sieve. The coating sequence of the rear half is a multi-level structure of graphene / molecular sieve / graphene, etc., and the channel surface layer is graphene.

[0045] Based on the above structure, a multi-level staggered structure scheme for the Rh catalyst and CeO2 co-catalyst, or a similar scheme, is proposed. A single-layer coating on the channel surface can be adopted, i.e., the Rh catalyst and CeO2 co-catalyst are directly coated on the surface of the graphene or molecular sieve channel. For example... Figure 3 As shown in (a), the Rh catalyst and CeO2 co-catalyst are directly coated on the surface of graphene or molecular sieve channels.

[0046] like Figure 3 As shown in (b), the Rh catalyst and CeO2 co-catalyst are applied in a multi-level, staggered manner within the structure and on the channel surface. Specifically, the Rh catalyst and CeO2 co-catalyst are also coated on the graphene or molecular sieve surface within the structure. The single-layer coating on the channel surface is similar to the structure of existing three-way catalytic converters, while the multi-level, staggered coating within the structure and on the channel surface further enhances the oxygen storage and release capacity of the adsorber, facilitating the regulation of oxygen molecules. The multi-layered Rh main catalyst and CeO2 co-catalyst structure increases the contact area between the catalyst and N2O, as well as the diffusion region within the pore structure, prolonging the N2O adsorption time and increasing the internal temperature of the N2O catalyst under low-temperature engine start-up conditions.

[0047] like Figure 4 As shown, in the exhaust gas components, N2O is a linear polar molecule; CO2 is a linear nonpolar molecule; H2O has a V-shaped polar molecular structure; and NH3 has a trigonal pyramidal polar molecular structure. Based on the structure and polarity of N2O molecules, the pore structure of molecular sieves can be controlled using the tunable pore structure of graphene, altering its structure and specific surface area to make the pore size and polarity suitable for the adsorption and diffusion of N2O molecules. The modified graphene / molecular sieve exhibits shape-selective adsorption and catalysis of N2O while reducing the influence of H2O and NH3, as shown in the figure. Figure 5 As shown.

[0048] In a preferred embodiment, the method for preparing the catalyst includes the following steps:

[0049] The methods for modifying molecular sieves with graphene are as follows:

[0050] 1) Using the in-situ hydrothermal synthesis method, the honeycomb cordierite ceramic carrier is placed in the prepared molecular sieve precursor solution and crystallized in situ at a certain temperature, so that the molecular sieve is directly "grown" on the carrier to obtain the molecular sieve coating.

[0051] 2) By directly adding hydrazine hydrate to the aqueous solution of graphene oxide and then reducing it with hydrothermal method, a graphene solution that is uniformly and stably dispersed in water is obtained, avoiding the addition of surfactants, organic solvents or superacids in the conventional preparation of stable graphene aqueous solutions.

[0052] 3) The honeycomb cordierite ceramic carrier with molecular sieve coating is placed in a graphene solution, and the graphene is highly dispersed into the surface and channels of the molecular sieve by ultrasonic impregnation, thereby completing the surface and channel modification of the molecular sieve and obtaining a graphene / molecular sieve coating.

[0053] 4) Further, by repeating the above steps, a multi-layered coating structure can be obtained.

[0054] A zero-emission N2O catalytic converter for a gasoline engine is constructed by encapsulating the aforementioned catalyst. This catalytic converter is positioned after the three-way catalytic converter in the gasoline engine's exhaust aftertreatment system, as shown in the diagram. Figure 6 As shown.

[0055] A schematic diagram of the structure of a gasoline engine N2O catalytic converter is shown below. Figure 7 As shown in the figure, (a) is an N2O catalyst; (b) is a radial cross-sectional view of the honeycomb structure inside the catalyst; (c) is a cross-sectional view of the central axial channel; (d) is a cross-sectional view of the boundary axial channel; and (e) is a diagram of the local surface structure of the channel.

[0056] The technical principle is as follows:

[0057] (1) Thermal properties

[0058] The thermal conductivity λ1 and thermal diffusivity a1 of graphene are much greater than those of molecular sieves, while the specific heat capacity c1 of graphene is less than that of molecular sieves, c2. After modifying molecular sieves with graphene, the thermal conductivity λ3, thermal diffusivity a3, and specific heat capacity c3 of the graphene / molecular sieve material should fall between those of graphene and molecular sieves, i.e.:

[0059] λ2<λ3<λ1; a2 <a3<a1;c1<c3<c2

[0060] This improves the thermal conductivity and thermal diffusion properties of the coating structure, thereby enhancing the thermal conductivity and thermal diffusion properties of the catalyst. Under the same low-temperature engine start-up conditions, it can rapidly increase the internal temperature of the N2O catalyst.

[0061] (2) Stability

[0062] Graphene has a very stable honeycomb lattice structure and superhydrophobicity, while molecular sieves have silicon-oxygen tetrahedral or aluminum-oxygen tetrahedral structures. After modifying molecular sieves with graphene, the structural stability and hydrophobicity of graphene / molecular sieve materials can be improved.

[0063] (3) Adsorption performance

[0064] The specific surface area S1 of graphene is much larger than that of molecular sieve S2. After graphene is used to modify molecular sieves, the specific surface area S3 of the graphene / molecular sieve material should be between that of graphene and molecular sieve, that is:

[0065] S2 <S3<S1

[0066] This can improve the surface and internal adsorption performance of the N2O catalyst.

[0067] (4) Catalytic decomposition process

[0068] A schematic diagram illustrating the physical and chemical processes of N2O in a gasoline engine N2O catalytic converter is shown below. Figure 8 As shown, it includes: the diffusion and adsorption process of N2O on the surface of the catalyst support channel coating and in the nanoporous material inside the graphene / molecular sieve structure, and the catalytic chemical reaction process of N2O on the surface of the coating and in the nanoporous material inside the graphene / molecular sieve structure.

[0069] The N2O catalytic decomposition reaction is as follows:

[0070] 2N₂O → 2N₂ + O₂ (1)

[0071] The possible reaction processes for the catalytic decomposition of N2O on a catalyst are as follows:

[0072] 1) N2O is adsorbed on the surface of the noble metal catalyst T*, yielding N2O*.

[0073]

[0074] 2) N2O* decomposes into N2(g) and adsorbed oxygen species O*.

[0075] N2O*→N2+O* (3)

[0076] 3) Through the Langmuir-Hinshelwood (LH) mechanism, adsorbed oxygen species recombine and regenerate vacancies.

[0077]

[0078] 4) N2O combines with the adsorbed oxygen species O* to obtain N2(g), O2(g), and the regenerated noble metal catalyst T*.

[0079] N₂O + O* → N₂ + O₂ + T* (5)

[0080] 5) N2O adsorbs on the surface of the noble metal catalyst T* and reacts to produce N2(g) and adsorbed oxygen species O*.

[0081] N2O+T*→N2+O* (6) Energy change ΔE during adsorption process ads :

[0082] ΔE ads =E catalyst+adsorbate -(E catalyst +Eadsorbate (7)

[0083] In the formula, E catalyst+adsorbate The energy of the adsorbate adsorbed by the catalyst, E catalyst It is the energy of the catalyst, E adsorbate It is the energy of the adsorbate.

[0084] Activation energy ΔE of the reaction process:

[0085] ΔE=E TS -E IS (8)

[0086] In the formula, E IS It is the total energy of the initial state, E TS It is the total energy of the transition state.

[0087] Reaction rate constant:

[0088]

[0089] In the formula, k B is Boltzmann constant, h is Planck constant, R is universal gas constant, T is temperature, and ΔE is activation energy of the reaction.

[0090] The gasoline engine N2O zero-emission catalyst and catalyst unit provided in this invention have the following advantages:

[0091] (1) The multi-level interlaced structure of graphene / molecular sieve modified by graphene changes the pore structure of the coating, increases the specific surface area of ​​the material, and is beneficial to increasing the adsorption capacity of N2O.

[0092] (2) Based on the size and polarity of N2O molecules, the structural tunability of graphene molecules is utilized to change the pore structure and adsorption polarity of molecular sieves, so that the modified graphene / molecular sieve pore structure has shape-selective catalytic properties for N2O.

[0093] (3) The multi-level interlaced structure and the increased specific surface area of ​​the material can change the diffusion performance of N2O in the pore structure and prolong the diffusion time, which is beneficial for the catalyst to have enough time to raise the temperature and reach the temperature of N2O catalytic decomposition.

[0094] (4) In the multi-level interlaced graphene / molecular sieve, graphene has very good thermal conductivity and thermal diffusivity, and low specific heat capacity, which is conducive to thermal diffusion and temperature rise inside the catalyst, and shortens the ignition time of the catalyst.

[0095] (5) The multi-level interlaced structure of Rh catalyst and CeO2 co-catalyst increases the internal active sites of the catalyst, which can improve the internal oxygen storage and release regulation capabilities of the catalyst and the catalytic performance of N2O.

[0096] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A catalyst for zero N2O emissions in gasoline engines, characterized in that: The catalyst uses Rh as the main catalyst and CeO2 as the co-catalyst, with graphene / molecular sieve modified by graphene as a multi-level coating and honeycomb cordierite ceramic as the carrier. The coating sequence on the cordierite carrier is a multi-level structure of graphene / molecular sieve / graphene, with the channel surface layer being graphene; or The coating sequence on the cordierite carrier is a multi-level structure of molecular sieve / graphene / molecular sieve, and the channel surface layer is a molecular sieve. The preparation method of the catalyst includes the following steps: (1) Using the in-situ hydrothermal synthesis method, the honeycomb cordierite ceramic carrier is placed in the prepared molecular sieve precursor solution for in-situ crystallization, so that the molecular sieve grows on the carrier and obtains the molecular sieve coating. (2) Add hydrazine hydrate to the aqueous solution of graphene oxide and then reduce it by hydrothermal method to prepare graphene solution, so as to obtain a graphene solution that is uniformly and stably dispersed in water. (3) The honeycomb cordierite ceramic carrier with molecular sieve coating is placed in graphene solution, and the graphene is highly dispersed to the surface and channels of molecular sieve by ultrasonic impregnation method to complete the surface and channel modification of molecular sieve and obtain graphene / molecular sieve coating after graphene modification of molecular sieve. (4) Repeat steps (1)-(3) to obtain a multi-layered coating.

2. The catalyst according to claim 1, characterized in that, The cordierite carrier is divided into two parts along the channel direction. The coating sequence of the front part is a multi-level structure of graphene / molecular sieve / graphene, and the channel surface layer is graphene. The coating sequence of the rear part is a multi-level structure of molecular sieve / graphene / molecular sieve, and the channel surface layer is molecular sieve.

3. The catalyst according to claim 1, characterized in that, The cordierite carrier is divided into two parts along the channel direction. The coating sequence of the front part is a multi-level structure of molecular sieve / graphene / molecular sieve, and the channel surface layer is molecular sieve. The coating sequence of the rear part is a multi-level structure of graphene / molecular sieve / graphene, and the channel surface layer is graphene.

4. The catalyst according to any one of claims 1-3, characterized in that, The Rh catalyst and CeO2 co-catalyst are directly coated on the surface of graphene or molecular sieve channels.

5. The catalyst according to claim 4, characterized in that, The Rh catalyst and CeO2 co-catalyst are also coated on the surface of graphene or molecular sieve inside the structure.

6. A catalytic converter for zero N2O emissions in a gasoline engine, characterized in that, It is encapsulated from the catalyst described in any one of claims 1-3.

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